RU2376106C2 - Method and device for manufacturing of metallic strips and sheets excluding discontinuity between continuous casting and rolling - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention is provided for manufacturing of metallic strips of thickness in the range 0.14-20 mm and metallic sheets of thickness in the range 10-100 mm from slabs of thickness 30-300 mm by means of continuous casting at curvilinear installation. Decreasing of slab's thickness is implemented with increasing from the process beginning in ingot-forming equipment up to stage of rolling. Slab at outlet from ingot-forming equipment allows inverted temperature gradient in cross section with medium temperature of slab surface less than 1150°C and with middle temperature of core more than 1350°C. After continuous casting slab is fed without destruction of continuity to stage of rolling after heating in induction furnace. Additionally feed rate from continuous casting to the end of rolling in discrete steps increases according to reduction of slab's thickness. Rolled flat production is cooled and it is implemented cutting of sheets or wind-up rolls. Between rolling mill it can be ubstalled additional cooling system.

EFFECT: ensured by compactness of installation it is implemented maximal usage of molten metal power, it is provided quality of final product.

9 cl, 3 dwg

Description

The invention relates to a method and a corresponding system for the manufacture of metal strips and sheets without disrupting the continuity of the process, from continuous casting of the melt to the last stand of the rolling mill, in particular for the manufacture of flat steel products, without manufacturing intermediate products.

In the steel industry, due to the significant increase in the cost of raw materials and energy used and due to increasing competition in the world market, as well as due to increasingly stringent anti-pollution standards, there is a need to develop a method for manufacturing high-quality hot-rolled coils and sheets, which requires less investment and the costs of making an increasingly thin strip. Due to this, it is possible to increase the competitiveness of the conversion operations of the final product with less energy, and at the same time reduce the harmful effects on the environment.

In this direction, in recent years, feasible technical solutions have been proposed, for example, according to patents EP 0415987, 0925132, 0946316, 1011896 addressed to this applicant, and also the international publication WO 2004/0262497.

But it turned out that the results obtained to date, although optimal in terms of product quality (especially the quality of steel strips), can be improved in terms of compact equipment layout and energy saving, and also in terms of a possible increase in the product range.

If we consider the concept of "continuous casting and rolling in one line", for example, according to the mentioned document EP 0415787 only at the first stage of the method and with only one stand of the rolling mill with a curved casting machine, then in this sequence an intermediate product is provided for which, after the stage heating, a second rolling step is required.

Also, according to a later document WO 2004/026497, the aforementioned “continuous casting and rolling technology in one line” combines continuous casting with the first rolling step containing no more than four stands to obtain intermediate products, which are then cut and, after the heating step, further processed by plastic stretching and in the second stage of rolling. According to this publication WO 2004/026497, it is also possible to remove sheets after the first roughing step, but without the controlled cooling system required to produce high quality sheets. In practice, the ability to remove sheets performs only the buffer function in case of malfunctions in the subsequent process - in order to avoid stops of continuous casting and the entire production line, but not in connection with the planned production of sheets.

The same idea of "continuous casting and rolling in one line" is also present in document EP 0823294, according to which three specific production steps are provided: the first stage of roughing in the austenitic phase - with the production of intermediate products; the second stage, which is an intensive heat treatment of this intermediate product to temperatures <738 ° C, with a phase transformation in the state diagram of iron - carbon; and the third stage is finishing rolling in the ferrite phase. The technical solution according to this document essentially consists in applying the concept of continuous casting and rolling in one line to obtain a strip of small thickness in three defined process steps, the last of which is carried out exclusively during the ferrite phase, thereby eliminating the possibility that the so-called “mass flow” "(That is, the amount of steel emerging per unit time from the continuous casting process) may be such that it becomes possible to obtain ultrafine products using one the production phase, carried out entirely in the austenitic region.

EP 0889762 also discloses the application of the concept of continuous casting and rolling in one line for the manufacture of thin strips in one step without breaking continuity, and discloses a method for combining the production step of continuous casting of a slab with a high mass flow rate (thickness of the slab in meters times the output velocity> 0.487 m ² / min) and with a high temperature (about 1240 ° C) at the exit of continuous casting, with the rolling step after the temperature homogenization step.

Just like EP 0823294, document EP 0889762 also actually provides that the cooling step or, alternatively, the heating step is carried out between the first roughing stands and the last finishing stands. The simulation and testing showed that the method according to this patent cannot be applied on an industrial scale. The idea of providing a high temperature (about 1400 ° C) for continuous casting to use the highest possible heat content at the next rolling stage is really interesting, but practically impossible, since it was found that when casting a slab with a high mass flow rate and at such a high temperature that the surface temperature at the outlet of continuous casting exceeds 1150 ° C, leads to disruptions in the meniscus area, thereby causing defects in the slab and increasing the risk of rupture chki.

The present invention solves this problem mainly with the help of a secondary cooling system, designed for a significant mass flow rate, and by providing induction heating, which provides an increase in the temperature of the slab by at least 100 ° C.

The purpose of the invention is to provide a production method for producing using an extremely compact installation in one continuous step, including continuous casting and rolling, without intermediate products, hot rolled strips, including ultra-thin thicknesses from a maximum of 20 mm to 0.14 mm; and high-quality sheets with a thickness of 10-100 mm with the maximum maximum use of all the energy supplied by the molten metal.

The method according to the present invention, the main features of which are set forth in claim 1, essentially includes a continuous casting step and a subsequent rolling step on a single production line, directly connected — without intermediate roughing — to the induction heating section provided between continuous casting and rolling .

Another objective of the invention is to provide a system or installation for performing the aforementioned method, in which the stands of the rolling mill operate without disrupting the continuity of the material, after continuous casting, behind an induction furnace; with a minimum distance between the exit from continuous casting and the first rolling stand. The main features of this installation are given in paragraph 4 of the claims.

Other aspects and features of the invention listed in the dependent claims are explained in the following detailed description of a preferred embodiment of the installation, with reference to the accompanying drawings, in which:

FIG. 1 schematically shows an example of an apparatus according to the invention for the manufacture of steel strips wound into a roll with a minimum thickness of up to 1 mm, or sheets with a maximum thickness of up to 100 mm.

FIG. 2 schematically shows a mold with preferred dimensional characteristics according to the invention.

FIG. 3 schematically shows a decrease in thickness, starting from the mold to the last rolling stand.

It should be noted that the description essentially relates to the manufacture of steel sheets and / or thin and ultra-thin strips of carbon or stainless steel material, but the present invention also applies to the manufacture of strips or sheets of aluminum, copper or titanium.

It is known that the melt (molten steel) is fed from the ladle to the intermediate casting device and from there to the mold of the continuous steel casting machine, while the thickness of the slab at the outlet, already reduced compared to the thickness at the entrance to the mold: 30 - 300 mm, and length 600 - 4000 mm. The reduction in thickness occurs in the presence of a liquid core with secondary cooling at the same stage of casting, as a result of which in rolling stands directly connected to continuous casting, the energy of liquid steel is used to the maximum extent at the beginning of the process until the desired thickness of 0.14 to 20 mm for strips and 10-100 mm for sheets.

It was found that in the present invention, the decisive moment is that the material flow or the “mass flow rate” mentioned above is high in order to provide the temperatures and speed required by the rolling process for the final product with the desired thickness and surface quality, with the desired internal quality ; and so that the decrease in thickness becomes more significant, starting with the mold. As seen in FIG. 3: the reduction in thickness begins in the mold itself, where the thickness of the slab is reduced for the first time in its central part, in which there is a part thickened in the middle, and the decrease in thickness continues in the lower part of the casting installation, where compression with a liquid core takes place, and ends in the last rolling crates. It should be noted that at the stage of thickness reduction during casting, the material feed rate is constant.

As seen in FIG. 2, the mass flow rate is proportional to the feed rate and the slab cross-sectional area S _B. In particular, to achieve the aforementioned objective of the invention, the optimal ratios are determined between the surface area S _{M of the} surface of the molten steel (or the melt, in general) in the mold taken in a horizontal section corresponding to the meniscus, minus the surface area S _T affected by the submerged casting glass, and the vertical the cross section S _{B of the} slab at the exit of continuous casting.

This ratio S _M / S _B must be greater than or equal to 1.1 to ensure limited flow rates of liquid steel (or, in general, melt), as a result of which turbulence in the mold and meniscus waves are minimized.

On the other hand, the increased consumption of liquid metal also entails the need to increase the secondary cooling energy of the slab. The prior art for this purpose proposes to increase the flow rate of cooling water. But it was found that an excessive increase in the consumption of cooling water as a result makes it difficult to drain the water itself, which can stagnate in front of the nozzles, as a result of which the uniformity of cooling necessary to ensure the quality of the final product is violated. It was found that with water pressure values of 15–40 bar and with a distance between nozzles and slabs of less than 150 mm, it is possible to provide more efficient cooling of the slab at a high “mass flow rate”, and also very good temperature uniformity (in both transverse and longitudinal directions) required for high quality end products. In the presence of these parameters, the jet of water from the nozzles better passes through the formed vapor film, which creates the effect of isolation between the slab and the cooling water (Leidenfrost effect).

Secondary cooling, controlled by the aforementioned method, makes it possible to cool the surface of the slab while maintaining the highest possible temperature in the middle part of the slab.

The goal is that by ensuring the average surface temperature of the slab at the outlet of continuous casting at values <1150 ° C, the so-called “buckling” effect, that is, buckling of the slab between the rolls of the casting machine, creating meniscus disturbances and subsequent negative consequences, can be eliminated for product quality; and also in order to have at the outlet of the casting machine the average temperature in the average cross section of the slab as high as possible and in any case more than> 1300 ° C in order to obtain the greatest possible reduction in thickness with the smallest breaking force during rolling.

This provides savings both in terms of reducing investment (smaller stands), and in terms of reducing the energy required for the same thickness of the final product. In this regard, it should be noted that according to the present invention, in contrast to installations according to the prior art, the non-excessive energy consumption is sufficient to obtain even more reduced final thickness values; the values in kilowatts are proportional to the thickness at the outlet of the casting (SpB). For example, for a slab of 1600 mm in size, the required energy for the first five stands is as follows:

1 stand: kW <SpB x 20

2 stands: kW <SpB x 40

3 stands: kW <SpB x 70

4 stands: kW <SpB x 85

5 stands: kW <SpB x 100

The foregoing is shown, for example, in FIG. 3, which schematically and in accordance with a successive decrease in thickness, shows an increase in energy consumption in the first five stands, in the form of an indication of the respective size of each of the stands.

Using a curvilinear filling machine, the height of which is lower than the vertical casting machine, the ferrostatic pressure inside the cured slab is lower for the same cross section and speed from the continuous casting outlet, as a result of which the buckling effect can be eliminated or minimized.

In FIG. 1 is an example of a plant according to the present invention, with a slab 1, at the exit of continuous casting after a crystallizer 10. A slab 1 of a thickness of 30-300 m and a width of 600-4000 mm is then fed to rolling step 11 through an induction furnace 12 for heating in front of the stands, and also through the descaler 16. The distance between the continuous casting outlet and the first mill stand 11 will not exceed 50 m in order to limit the temperature loss of the slab; and this provides additional benefits of providing a more compact installation with less space required for it. The feed rate for the entire process from continuous casting to the last stand increases and corresponds to the reduction in thickness required for the desired final product; while the mass flow rate is constant. The rolling mill 11 in this production line consists of one or more stands that provide the desired final thickness; for example, in FIG. 1 shows seven stands (V1-V7). The mill rolls have a preferred diameter of 300-800 mm. This arrangement provides a corresponding reduction in thickness according to the thickness of the final product and also very good cooling of each roll to prevent cracking from heating.

The installation in accordance with the invention, in particular the rolling mill 11, starting from continuous casting 10 has a speed control system in a subsequent cascade where there is a device 14 that cuts the coils being wound onto the final winder after the final cooling system 13. Before this system, the cutting device 14 ', which works as an alternative to the other, provides the possible removal of sheets 20 and can be installed earlier in the production line after fewer stands compared to those shown in the drawing; taking into account the greater thickness usually expected for sheets (up to 100 mm) compared to strips.

An adjustable cooling system is also provided that cools the sheets of the cutting device 14 ′.

In addition to the strip cooling system 13 in front of it, at least one cooling system is provided in line for cooling the surface of the slab 1, which is schematically shown in the figure by opposite arrows (as in 13) between two adjacent stands, forming the so-called inter-cell cooling 13 'for secondary oxidation limits.

As mentioned above, the feed rate in the whole process from continuous casting to the last stand increases in stages and corresponds to a decrease in thickness in accordance with such characteristics as the thickness and quality of the desired final product. To this end, a speed control system is provided in a cascade in the direction of material flow, starting from continuous casting, and the control method can be described as the opposite to that used in rolling mills according to the prior art, where the control was a cascade in the upward direction.

This is a cascade control in the "up" direction, if it is used either for installation according to the present invention, or for methods and installations according to other patents (in particular, EP 08897562), with continuous casting directly connected to the rolling step without breaking continuity, this will inevitably cause a change in casting speed - with negative consequences for the quality characteristics of the slab in terms of surface uniformity and internal characteristics of the material.

Therefore, eliminating the general technical drawback, a new approach to regulation in the cascade in the direction of the material is adopted, according to which the casting speed is set, and possible speed adjustments affect the speed parameters of subsequent stands, also taking into account the operational differences of the stands in the installation according to the invention with respect to the subsequent . According to the prior art, the strip enters each stand when it is already closed, with pressure between the rollers depending on the thickness required by the standard passage; while the regulation in the cascade in the direction of "up" leads to the adjustment of the speed in the stands, already pressing the material. On the contrary, in the method and installation according to the invention, the slab enters each stand with open rolls that are closed by passing the front of the slab until a pressing corresponding to the required thickness reduction is achieved.

An example of a change in process parameters (thickness,% reduction in thickness, temperature and speed) is shown schematically in FIG. 1, in accordance with the different positions of the inlet and outlet of the induction furnace 12, descaling machine 16 and rolling stands. For this purpose, the designations IN OUT are used in accordance with the designations IN for the induction furnace and DES for the descaler, respectively; and also V1-V7 for the different stands shown in FIG. 1. For stands, the values of the four output parameters are only indicated, with the exception of the first stand V1 of the mill, where the values at the inlet are also given. In particular, it can be noted that in accordance with the invention: if, for example, you start with a slab with an initial thickness of 70 mm and an initial speed of 6.5 m / min, then a thickness of about 1 mm can be obtained in a plant with a total length of 70 m It can also be noted that the temperatures of the strip at the exit from the last stand are such that they provide rolling during the austenitic phase.

It can also be noted that the method according to the invention and its corresponding installation can be used for the manufacture of continuous strips and sheets not only of carbon or stainless steel, but also of aluminum, copper or titanium.

Claims (9)

1. A method of manufacturing metal strips with a thickness of 0.14-20 mm and metal sheets with a thickness of 10-100 mm, including obtaining slabs by continuous casting on a curvilinear installation directly connected to rolling in a single production process without disrupting the continuity, induction heating of the slab between casting and rolling , a phased decrease in the thickness of the slab, characterized in that continuous casting receive slabs with a thickness of 30-300 mm and a width of 600-4000 mm, a decrease in the thickness of the slab is carried out with increasing from the beginning of the process in the mold and continue at the stage of casting and rolling, while providing secondary cooling of the slab to obtain at the outlet of the installation of continuous casting slab having an inverted temperature gradient in cross section with an average surface temperature of the slab less than 1150 ° C and with an average core temperature of more than 1350 ° C, carry out controlled cooling of the rolled strip and the subsequent cutting and removal of sheets after controlled cooling or a section of rolls wound on a coiler, after the final cooling REPRESENTATIONS, the speed, starting from continuous casting is adjusted in the direction of material cascading sequence with gradual increase of casting speed to rolling end in accordance with the reduction of the slab thickness, and the distance between continuous casting and rolling is adjusted. 2. The method according to claim 1, characterized in that at least one additional step of controlled cooling of the surface of the slab during rolling is carried out. 3. The method according to claim 1, characterized in that the slab is obtained with a thickness of more than 30 mm and at a speed of more than 4 m / min. 4. Installation for the manufacture of metal strips with a thickness of 0.14-20 mm and metal sheets with a thickness of 10-100 mm, containing a curvilinear continuous casting unit with a mold and means for compressing a slab with a liquid core, a finishing rolling mill directly connected to the continuous casting unit, furnace (12) induction heating, located between the continuous casting plant and the rolling mill (11), characterized in that the installation is equipped with a secondary cooling system for the slab having a thickness of 30-300 mm and a width of 600-400 0 mm, to obtain a slab having an inverted temperature gradient in cross section with an average slab surface temperature of less than 1150 ° C and with an average core temperature of more than 1350 ° C, a cooling system (13), a device (14) sections of rolls wound on a final winder (15) after the cooling system (13), or by a device (14 ') for cutting and removing sheets (10) cooled by the cooling system (13), the mold being made with a ratio of the cross-sectional area S _M at the meniscus minus the occupied decomp paid-glass area S _T to the cross-sectional area at the outlet of the crystalliser than or equal to 1.1, the maximum length of the finishing mill is 50 m. 5. Installation according to claim 4, characterized in that the rolling mill (11) is formed from at least one stand, a maximum of twenty stands, while the energy required for the first five stands is determined depending on the thickness of the slab emerging after casting , by multiplying this value by increasing coefficients from 20 for the first stand to 100 for the last stand - with a slab width of 1600 mm, while for higher values of the slab width, these coefficients increase in proportion to the ratio between the actual width and 1600 mm. 6. Installation according to any one of paragraphs.4 and 5, characterized in that it is equipped with an additional system (13 ') for cooling the surface of the slab, pressurized water located between at least two adjacent rolling stands and equipped with nozzles, facing the slab (1). 7. Installation according to claim 4, characterized in that the water pressure during secondary cooling is 10-40 bar, and the distance from the cooling nozzles to the slab (1) is less than or equal to 150 mm. 8. Installation according to claim 4, characterized in that the rolls in the stands (11) of the rolling mill have a diameter of from 300 to 800 mm. 9. Installation according to claim 4, characterized in that the device (14 ') for cutting and removing sheets (20) is located after the cooling system (13') located between the stands, and in front of the cooling system (13), and the device (14) ) pieces of rolls wound on the final winder (15), made in the form of scissors.

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